1. Field of the Invention
The invention relates to a digital time base corrector in an apparatus for reproducing a video signal recorded on a recording medium.
2. Description of Background Information
When a video signal recorded on a video disc is simply demodulated and reproduced, fine jitters are included in the reproduced video signal due to an eccentric component of the video disc and the vibration of the mechanism system. This results in a time base error which causes a deviation of the reproduced video signal from a reference time base. As means for correcting such a time base error, there is known a digital time base corrector such that after the reproduced video signal was converted into the digital data by an A/D converter, it is written into a memory, and the digital data is sequentially read out synchronously with a reference timing signal in accordance with the writing order and is converted to an analog signal by a D/A converter.
As a conventional digital time base corrector, there is a corrector disclosed in Japanese Patent Kokai No. 1-93273. In such a time base corrector, there is provided a phase locked loop (PLL) circuit such that at least one of a horizontal sync signal and a color burst signal is separated and extracted from the reproduced video signal and the separated signal is supplied to the PLL circuit. The PLL circuit produces a clock signal whose phase is synchronized with a time base error included in the reproduced video signal, and the clock signal is phase-modulated by phase modulating means in accordance with a phase comparison output of phase comparing means in the PLL circuit. The clock signal after completion of the phase modulation is used as a sample timing signal of the A/D converter. The clock signal, consequently, also traces the high frequency component of the time base error and the correction is performed.
In such a conventional digital time base corrector, however, when there is a phase comparison output in the phase comparison means, namely, even in a generating period of time of the horizontal sync signal and the color burst signal, the clock signal is phase-modulated in accordance with a phase error of the color burst signal, so that there is a problem such that residual errors cannot be eliminated.